This invention relates to flexible electrical cables in general and in particular to the mechanical design of a type of control cable which is employed in container loading devices, known as a spreader cable.
For the operation of machinery, transport and conveyor installations, flexible electrical cables have been developed in which, in a control cable design, the conductors are twisted in layers to form the core of the control cable over which suitable layers are provided. In the center of the cable, a carrier member in the form of a steel cable or a cable of non-metallic materials which does not exhibit much stretch when placed in tension can be arranged (VDE Specification 250 c/8.75, para. 814). Non-metallic materials which can be used for this purpose include for instance, fibers with an aramide base (German Journal "Kunststoffe", 1982, Page 486). Such a flexible cable can be used in a container loading facility (German Journal "Siemens Energietechnik", 1983, Pages 188 to 191) in such a manner that when the lifting device is moved, the cable is continuously deposited in a funnel when moving in one direction and taken up again when moving in the other. In this process the cable is freely conducted vertically through the air over a fairly great height. Under unfavorable weather conditions, especially in a wind storm, the cable can be heavily bent, which impedes the motion cycle of the cable.
For elevator control cables, a cable design is known in the art in which five conductors are always twisted around a high tensile strength central member to form a bundle and in which six of such conductor bundles are twisted around a carrier member. The core so formed and equipped with textile inserts is surrounded by wrapping and a plastic jacket. This cable design is distinguished by great flexibility, high bending strength and absolute stability of the conducting assembly (German Journal "Elektrodienst",. 1983, No. 1, Pages 26/27). For adapting an elevator control cable to the technical development in the field of electronic control and to the use of microprocessors, a cable design is also known in which the conductors have a small cross section and are twisted in one layer about a central element which consists of a load cord. With this heavy central element of large weight, the influence of the insulating and jacket materials on the running and suspension behavior of the cable is reduced (DE-OS No. 31 39 018).
Starting with a cable with the features described above in German Journal "Elektrodienst", it is an object of the present invention to improve the physical conductability of the cable in such a manner that the cable construction is better able to withstand wind forces and to thereby make possible the use of this cable as a "spreader cable".